The creation of the meta-tag "description" should now be bullet-proof against all types of plugins connecting to get_the_excerpt() and / or the_excerpt_rss().
A small change to the former behaviour:
If post_excerpt exists, it is used to create the meta-tag. Otherwise the meta-tag is created using a protected version of the_excerpt_rss.
Let me know, if you have any problems with this new revision.